The 'Leopard upgrade disc' should work fine. I've seen many reports of people having a fair amount of success. The only warning is that you might have much better results doing a fresh install (i.e. format hard drive before installing Snow Leopard) rather than an upgrade from Tiger. Of course, you'd need to do a full backup of everything important on your computer before doing this!
There has been some question over the strict legality of doing this, but I'm on the side that there's nothing bad about it - given that you're not permitted, by the EULA, to use a Leopard upgrade disc on anything but a computer with Leopard but the $30 Snow Leopard package is not labelled as an upgrade disc anywhere on the packaging or the included materials - just in the marketing publications.